National Audit Office report (51 pages, PDF) on the accounts of HM Revenue and Customs for the financial year 2007/2008.

In relation to excise duty fraud, the paper reports that:

[HMRC has] revised its methodology for estimating the illicit spirits market. The United Kingdom is one of the few countries to try to make such estimates, which are inherently difficult. The Department has not yet found an acceptable method for measuring potential tax gaps for other alcohol products, such as beer and wine, which in total comprise around 60 per cent of the duties collected. The Department recognises that it needs to do more and is working with the industry to establish a robust methodology to estimate the extent of the illicit market for all alcohol products.